Screw implant for a jawbone

ABSTRACT

A screw implant for a jawbone has a conical threaded implant body with an implant neck and a conical implant post to accept a replacement tooth or a substructure. The thread of the implant body is a compression thread with concave thread turns. 
     The implant neck preferably defines a bending zone wherein the ratio of the diameter D B  to the length L B  of the bending zone is in the range of 1:1.5 to 1:3. The bending angle is up to 30 degrees and the number of bendings of the bending zone is 3 to 4, when the implant post is bent back and forth. The implant neck has broadening transition sections.

CROSS-REFERENCE TO RELATED APPLICATON

This is a continuation-in-part of copending application Ser. No.07/436,594 filed Nov. 15, 1989, now U.S. Pat. No. 5,074,790 issued Dec.24, 1991, the entire disclosure of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a screw implant for a jawbone comprising athreaded conical body which can be screwed into the jawbone, on which isformed an implant neck and a conical implant post to accept areplacement tooth or a substructure.

2. Description of Related Technology

There are many forms of known tooth implants. Only a few of these havefound practical application. For example, needle implants and blade orplate and screw implants have been used. Even though screw implants havebeen found to be especially useful, they have not fulfilledexpectations. Proposed forms of such implants have been found to bedeficient, especially because of insufficient anchoring, damage to thebone, or because of complicated insertion methods.

German Offenlegungschrift 22 55 916 (May 16, 1974) describes a screwimplant which has a helical thread as well as a substantially constantoutside diameter. Good initial anchoring is taught to be achievable andthe anchoring effect is intended to improve as time progresses. However,it has been found that, since the diameter of the shaft is relativelylarge, the thread of the shaft cuts into the bone bed duringimplantation such that destruction of bone tissue cannot be avoided.Voids formed in the threads have an adverse influence on the lifetime ofthe implant, and also form infection sites. Furthermore, the rigidscrew-in implant cannot be bent, as for straightening, afterimplantation. As a rule, it is only possible to shorten such an implantby grinding of the column or post carried by the implant neck. This isespecially unpleasant for the patient, since the grinding has to be doneafter the insertion of the implant.

Another embodiment of a screw implant as described in Grafelmann, et al.U.S. Pat. No. 4,406,623 (Sep. 27, 1983) has a conical screw shaft with ahelical thread. The purpose of this structure is to impart to theimplant enhanced strength in the implanted state. It is clear from thispatent that, in screw implants, the form of the thread is of specialimportance, and very precise data are given. V-shaped sections are cutout from the threads of the helical thread winding at angular distanceswhich are smaller than 3600 but not equal to 1800. These cuts areradially directed and, starting from the periphery of the helix, thetips are in the region of the shaft surface. Furthermore, sharpenedparts which extend in the direction of insertion are formed. Thus, avery sharply cutting thread is provided and such an implant cuts intothe bone relatively deeply. However, this results in bone tissuedestruction and development of void spaces. Moreover, straightening ofthe implant is not possible and here, too, grinding processes must beemployed for adaptation.

German Offenlegungschrift 26 00 639 (Jul. 15, 1976) describes an insertfor a tooth bed wherein the insert has a nonbendable strengtheningextension and a thread, with the threads being cut deeply in such a waythat, upon insertion, voids are formed between the insert and thetissues which may lead to inflammation.

A screw-type jaw implant made from ceramic materials is described inMuench U.S. Pat. No. 4,468,200 (Aug. 28, 1984). At a lower end, which isintended for anchoring in the jawbone, a conical screw having a roundedend is provided, and at its upper end is a hollow groove for attachmentof the epithelial sleeve and which has an opening to accept a toothsupport. This is designed for insertion immediately after a tooth isextracted. There is an annular thickened portion between the upper andlower ends, which is designed as a conical screw and there are at leasttwo annular notches, whereby the diameter of the annular thickenedregion is smaller than the diameter of the thread peaks at the uppermostthread of the lower part of the jaw implant. In order to achieve anespecially secure anchoring, the lower part of the jaw implant isprovided with saw tooth-like threads but a disadvantage of these is thatthe jaw tissue is damaged when the implant is inserted. The threaddesign does not permit elimination of voids. Moreover, the securingsection for holding the replacement tooth cannot be adjusted.

Niznick U.S. Pat. Nos. 4,645,453 (Feb. 24, 1987) and 4,758,161 (Jul. 19,1988) disclose a dental implant consisting of two parts comprising ananchor and a special bendable adapter which is inserted into the anchorafter the anchor is fixed in the jawbone. The bendable adapter may bemade of titanium, a titanium alloy, stainless steel or, in U.S. Pat. No.4,758,167, a thermoplastic material and is bent to a degree determinedby prior study and survey. As a result, the location of the adaptor tobe bent must be carefully studied and the bending operation must beeffected outside of the mouth.

It has long been known that an implant must be anchored permanently. Inaddition to eliminating or minimizing void spaces in the bone tissue,the implant should be supported at both ends in the bone, that is, itmust be supported by the compact bone tissue of the alveolarcountercorticalis. However, as a rule, the formation of voids can onlybe prevented when, during the insertion of the screw implant, there isno destruction of the bone tissue through which it travels. In the caseof prior known screw implants, this cannot be prevented due to therelatively deep penetration of the cutting threads. However, as a resultof the destruction of tissue and the development of voids around theimplant, primary stability, on which later retention depends and whichis responsible for a strong bond between the implant and bone, is notensured. Especially in the front tooth region of the lower jaw, thelength of the screw implant determines the degree of support by the bonetissue against which the implant lies during insertion. Therefore,either an implant with an accurate length must be used, or the end thatprotrudes from the jaw (i.e. the implant post) must be shortened orground to the proper size.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more of the problemsdescribed above.

According to the invention, a screw implant is provided which can beinserted simply and without destruction or damage, without formation ofweakening voids in the bone tissue and, as a result, which providesprimary strength so that the implant can be used immediately afterinsertion. The screw implant can also be adapted by straightening of theimplant post after the insertion of the implant.

Other objects and advantages will be apparent to those skilled in theart from a review of the following detailed description, taken inconjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation of a screw implant of the invention;

FIG. 2 is an elevation of the screw implant of FIG. 1 having a bentimplant post;

FIG. 3 is an enlarged elevation of the neck of the implant of FIGS. 1and 2; and,

FIG. 4 is a section of the screw implant of FIG. 1 taken along the lineIV--IV in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The screw implant of the invention has an implant body comprisingcompression threads having a concave design, as described in more detailbelow.

Referring to the drawings, the screw implant has a conical implant body,generally designated 1, with a compression thread 2 defined by concavethread turns 3. The implant body 1 is characterized by an outer boundarycone defining a cone angle α₁. The thread core is also conical anddefines an inner cone having a cone angle α₂. A spherical tip 2a isdefined at the lower end of the body 1.

The thread turns 3 are not necessarily circular, and have a maximumdepth 3a which is preferably about one third of the height of the threadturns 3.

As shown in more detail in FIG. 2, the thread turns may be circular witha radius r_(G) which is equal to about half of the thread pitch h. (Inthe drawings, the dimensions are not to scale.) An implant shoulder 4extends from the upper end of the compression thread 2. The shoulder 4has an implant neck, generally designated 5, which defines a bendingzone 6. The length of the bending zone 6 is designated L_(B) and thediameter is designated D_(B) (FIG. 3). An implant post 7 is defined atthe upper end of the neck 5.

As shown in FIG. 3 on a larger scale, the implant neck 5 has twotransition regions 10 and 11 which widen in the direction of the implantpost 7 and the implant shoulder 4, respectively, and have a radius ofcurvature r_(A), which can be the same magnitude for both transitionregions 10 and 11. The implant post 7 narrows conically upward and, atan upper end region, defines two flat opposed areas 8. The flat areas 8form a rectangle which serves for coupling an instrument or tool, whichis used as an aid for screwing in the implant, and for bending andstraightening the post 7. A hemispherical head 9 is formed on theimplant post 7. The cone of the implant post 7 (as seen from the tipedge) continues over the entire length of the post 7 withoutinterruption, so that the guidelines as edges 12 (FIG. 4) are retained.

In a preferred form, the implant post 7 is formed so that it defines aconical form with an upper spherical head. Flat areas 8 may be cut intothe conical form such that the common edge of two flat areas 8 isdisposed on the conical portion of the implant post as a retainedguideline (edge) 12, as described above with reference to FIGS. 1 and 4.

Since the flat areas 8 are cut into the conical portion of the implant,there is no interference of the rectangular arrangement by inserting asubstructure onto the implant.

The flat areas 8 need not define a rectangle in cross-section. Otherarrangements are possible, particularly six-sided (hexagonal)structures, or the like. The key of the bending and straightening orscrewing tool may be rectangular for use with either a rectangular orhexagonal screw head.

FIG. 2 shows the implant post 7 bent at an angle α_(B) to define a curvewith a radius of curvature r_(B) in the region of the bending zone 6.The radius r_(B) is typically between 2 and 3 mm. Although a bendingangle of up to 30 degrees is possible without damaging the implant neck,the bending zone 6 can be kept small if desired.

Since no alterations of the implant post 7 need be made before or afterinsertion thereof, standardized transfer caps with an inner conecomplementary to the implant post 7 can be used. As a result, an exactimpression can be made of the corresponding jaw region. Since the coneof the impression pin corresponds to that of the implant post 7, theimpression gives the position of the implant precisely. Thus, theprimary structure or substructures to be supported by the post will fitexactly.

The screw implant is formed of a metallic material such as corrosionresistant steel, titanium or the like, and is preferably formed of atitanium alloy and its surface is preferably passivated with protectivelayer of titanium oxide according to ASTM F 86-68.

After passage of the screw implant through the compact bone tissue ofthe alveolar chamber during insertion, the concave shaped compressionthread of the screw implant subjects the spongy bone tissue to agradually increasing pressure which results in extraordinarily highprimary stability even during the screwing-in process. The bone tissuesurrounding the implanted body is deformed within its elastic range, butis not destroyed.

The cone angle of the external boundary cone, α_(r), must be in acertain range of values. It has been found that deformation of the bonetissue remains within the range of elasticity of the bone tissue whenthe angle α₁ is between 2 and 4 degrees, preferably between 2.7 and 3.5degrees. Moreover, the design of the threads must be adapted to theangle α₁ and to the elasticity of the bone tissue. It has been foundthat it is preferable when the ratio of the cone angle α₁ of theexternal boundary cone to the cone angle α₂ of the cone encompassing thethread core of the compression thread is in the range of 1:0.6 to 1:1. Apreferred ratio is 1:0.85. The maximum outside diameter of the thread is2 to 2.5 mm, which depends on the area of application (for example,molars).

When the concave design of the threads is substantially in the form of acircular arc, there is a gradual radial displacement of bone tissuewhich fills the rounded area between the helical threads, so that novoids occur and thus the adverse consequences thereof can be avoided.According to a preferred embodiment, the radius of curvature r_(G) ofeach thread turn is greater than or equal to one-third of the threadpitch h. A preferred value is r_(G) =h/2. The thread pitch h is 1.3 to1.8 mm, preferably 1.5 mm.

The concave design of the thread turns can but need not be circular, andmay be, for example, oval or designed in some other way. In this case,the greatest depth of the individual thread turns is preferably smallerthan one-third of the thread pitch.

A thread designed with these parameters provides secure anchoring of theimplant body in the jawbone and is at the same time designed to beadapted to the elasticity properties of the bone tissue, so that novoids are formed between the bone tissue and implant body.

The implant shoulder 4 formed at the upper end of the implant body 1facilitates and improves straightening of the implant post afterinsertion of the implant.

Preferably, the ratio of the diameter D_(B) to the length L_(B) of thebending zone 6 is in the range of 1:1.5 to 1:3. A ratio of 1:2.6 isespecially advantageous. The diameter in the bending zone generally liesin the range of 1.5 to 2 mm, preferably 1.7 mm. Surprisingly, it hasbeen found that, at these lengths and ratios, a relatively large bendingangle (i.e., up to 30°) can be achieved, whereby the size of the bendingzone can be kept small, which is of special importance due to thetightness of the space conditions in the jaw region. The large bendingangle that can be achieved has the advantage that the bore, which isscrewed into the implant, does not have to be straightened in aprescribed manner with respect to the tooth replacement to be inserted.Regarding the straightening of the bore axis, the requirements are notas strict as in prior screw implants. This means that the bores can bemade more continuously than the bores for prior screw implants.

Since the screw implant is screwed-in until the bending zone lies in theregion of the gums, it is advantageous that the bending radius r_(B) inthe bending zone is smaller than or equal to 3 mm when the bending angleis equal to 30°. This small bending radius permits that the bending atthe gum region is limited.

In order to make it possible to correct an already straightened implantpost, it is important that the number of bendings of the bending zone,when the implant post is bent back and forth at a bending angle of 30degrees, is approximately 3 to 4. This means that it is possible tostraighten the implant head several times without the implant neckdeveloping cracks or without the implant post breaking off completely.This permits much more exact work than with the screw implants of theprior art.

In spite of the high flexibility offered by the screw implant accordingto the invention, the tensile strength of the implant neck can still beat least 2400 N at a bending angle of 30 degrees.

According to a preferred embodiment, the implant neck has at least onewidening transition section which borders on the bending zone and has aradius of curvature r_(A) of 2 to 3 mm. This transition region can bearranged either between the bending zone and the screw thread or betweenthe bending zone and the implant post. Since, as described above, theimplant neck with the bending zone lies in the region of the gum, it isespecially important that, after straightening the implant post, the gumlies tightly at the implant neck without the development of voids. Aradius of curvature of 2 to 3 mm in these transition regions permits oneto prevent the development of voids, due to the elasticity properties ofthe gums.

Due to the shape of the implant body, automatic centering occurs duringthe insertion process according to a predetermined bore channel. Thediameter of the implant is kept small.

In order to insert the implant, a preliminary bore is made with a smallimplant drill, the diameter of which is smaller than the largestdiameter of the implant body. This is a small intervention in which thebone tissue is not cut and only very little bone tissue is removed. Theimplant is then introduced axially through the prebored implant bed.

In order to facilitate insertion of the implant body, the two opposedflat areas 8 at the upper end of the implant post 7 accept a rectangularkey of a straightening device.

With the aid of a probe, the depth of the alveolar chamber to thecountercorticalis can be accurately measured and established through thebore channel and thus the length of the implant body can be determined.In case the implant to be inserted is somewhat longer than the basechannel, the implant can be shortened by grinding the implant foot tothe required length. Care must be taken that the implant foot isspherical so that it can be supported on the countercorticalis withoutdamage to the bone tissue. The radius of the spherical tip 2a ispreferably 0.5 mm.

The final insertion of the screw implant can be done in simple,continuous working steps, namely by preboring a narrow channel, orimplant bed, measuring the required length of the implant body and, ifnecessary, shortening this body at the implant foot, screwing-in of theimplant and straightening of the implant post. With the screw implantaccording to the invention, one can always achieve optimum accuracy ofadaptation and implant position. During the bending process, adjustmentparallel to the other teeth or vertical to the ridge of the jaw can bechecked and compared.

From the foregoing description, those skilled in the art will appreciatethat, in constrast to implants of the prior art such as disclosed inNiznick U.S. Pat. No. 4,645,453 and 4,758,161, the bending operationwith the implant of the invention is effected after fixing of theimplant into the jawbone within the mouth. The inventive implantcomprises a one piece homogeneous structure. Furthermore, the inventiveimplant defines an implant post which comprises a coupling area fordifferent tools which can be used in particular for screwing, bending orstraightening of the implant.

The foregoing detailed description is given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications within the scope of the invention will beapparent to those skilled in the art.

I claim:
 1. A screw implant for a jawbone comprising a threaded conicalimplant body adapted to be screwed into a jawbone,an attachment definingan implant neck and a conical implant post to accept a replacement toothor substructure, and, an implant shoulder being formed at the upper endof said implant body, said shoulder extending into said implant neck anddefining a bending zone, said implant post comprising a coupling areaadapted to be actuated by a screwing, bending, or straightening tool,said screw implant being defined by a single piece of a metallicmaterial and said bending zone including means for bending by the actionof said bending tool in the implanted state.
 2. A screw implant of claim1 wherein said implant body comprises a compression thread comprisingconcave thread turns.
 3. The screw implant of claim 2 wherein thegreatest depth of said individual thread turns is about one-third of thepitch h of said thread.
 4. The screw implant of claim 2 wherein saidthread turns have the shape of a circular arc and a radius of curvaturer_(G) of each thread turn greater than or equal to one-third of thepitch h of said thread.
 5. The screw implant of claim 4 wherein saidradius of curvature r_(G) is equal to h/2.
 6. The screw implant of claim1 wherein said implant post is formed on a conical broadening region ofsaid implant neck.
 7. The screw implant of claim 6 wherein the number ofbendings of said bending zone is 3 to 4 when the implant post is bentback and forth by 30 degrees.
 8. The screw implant of claim 6 whereinsaid conical broadening region extends over the entire length of saidimplant post without interruption so that the guidelines are retained.9. The screw implant of claim 1 wherein said bending zone has a diameterD_(B) and a length L_(B), the ratio D_(B) :L_(B) being in the range of1:1.5 to 1:3.
 10. The screw implant of claim 1 wherein said implant neckhas at least one broadening transition region bordering the bending zoneand having a radius of curvature r_(A) of 2 to 3 mm.
 11. The screwimplant of claim 1 wherein said bending zone has a bending radius r_(B)of less than or equal to 3 mm at a bending zone angle α_(B) of 30degrees.
 12. The screw implant of claim 1 wherein a free end of saidimplant post defines a spherical head.
 13. A screw implant for a jawbonecomprising a threaded conical implant body adapted to be screwed into ajawbone, said implant body comprising a compression thread havingconcave thread turns wherein said compression thread defines an outerboundary cone having an angle of opening α₁ and a core having a coneangle α₂, the ratio of α₁ :α₂ being in the range of 1:0.6 to 1:1,anattachment defining an implant neck and a conical implant post to accepta replacement tooth or substructure, and, an implant shoulder formed atthe upper end of said implant body and extending into said implant neckand defining a bending zone, said implant post comprising a couplingarea adapted to be actuated by a screwing, bending, or straighteningtool, said screw implant being defined by a single piece of a metallicmaterial and being bendable in the bending zone by the action of saidbending tool in the implanted state.
 14. A screw implant for a jawbonecomprising a threaded conical implant body adapted to be screwed into ajawbone,an attachment defining an implant neck and a conical implantpost to accept a replacement tooth or substructure, and, an implantshoulder being formed at the upper end of said implant body, saidshoulder extending into said implant neck and defining a bending zone,said implant post formed on a conical broadening region of said implantneck and comprising a coupling area adapted to be actuated by ascrewing, bending, or straightening tool, wherein the tensile strengthof said implant neck is at least 2400 N at a bending angle α_(B) of 30degrees, said screw implant being defined by a single piece of ametallic material and being bendable in the bending zone by the actionof said bending tool in the implanted state.
 15. A screw implant for ajawbone comprising a threaded conical implant body adapted to be screwedinto a jawbone,an attachment defining an implant neck and a conicalimplant post to accept a replacement tooth or substructure, and, animplant shoulder being formed at the upper end of said implant body andextending into said implant neck and defining a bending zone, saidimplant post comprising a coupling area adapted to be actuated by ascrewing, bending, or straightening tool, said coupling area comprisingtwo flat areas opposite to one another in order to accept a rectangularkey of said tool, said screw implant being defined by a single piece ofa metallic material and being bendable in the bending zone by the actionof said bending tool in the implanted state.
 16. A screw implant for ajawbone comprising a threaded conical implant body adapted to be screwedinto a jawbone,an attachment defining an implant neck and a conicalimplant post to accept a replacement tooth or substructure, and, animplant shoulder being formed at the upper end of said implant body,said shoulder extending into said implant neck and defining a bendingzone having a diameter D_(B) and a length L_(B), the ratio D_(B) :L_(B)being in the range of 1:1.5 to 1:3, said bending zone further having abending radius r_(B) of less than or equal to 3 mm at a bending zoneangle α_(B) of 30 degrees, said implant post comprising a coupling areaadapted to be actuated by a screwing, bending, or straightening tool,said screw implant being defined by a single piece of a metallicmaterial and being bendable in the bending zone by the action of saidbending tool in the implanted state.